Which nerve injury is associated with the claw hand deformity?

The claw hand deformity is primarily associated with injuries to the median and/or ulnar nerves. This condition occurs due to the loss of function in the intrinsic muscles of the hand, which are primarily innervated by these nerves. When the ulnar nerve is affected, it results in the inability to fully extend the fourth and fifth fingers because the interosseous muscles and the ulnar half of the flexor digitorum profundus are weakened. This leads to hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints, producing the characteristic "claw" appearance.

In cases where the median nerve is also involved, the first three fingers may exhibit similar issues, compounding the claw-like appearance. The position results from the unopposed action of the extrinsic muscles, predominantly flexors, which continue to function while the intrinsic muscles are compromised.

Other nerve injuries mentioned, such as radial nerve injuries, typically result in wrist drop and do not cause claw hand. The axillary and musculocutaneous nerves primarily affect shoulder mobility and forearm function, respectively, but are not involved in hand intrinsic muscle function, thus not contributing to a claw hand deformity. Consequently, the